The present invention relates to an electrical machine with axially directed magnetic flux.
Electrical machines with axially directed flux have been subjected to many constructional problems. In this type of machines, the flux propagates in three dimensions which causes big problems with flux leakage. Traditional electrical steel sheets are not convenient for flux in several dimensions. Further, the design of the winding has caused cooling problems. Available constructions within the area are complicated to manufacture. Known machines have problems with both vibrations and high sound level. Machines according to known technique furthermore have problem with high starting torque.
The present invention intend to solve the above mentioned problems. The object is to provide an electrical machine with axially directed flux with low flux leakage, low vibrations and low starting torque, which is easy to manufacture and useful in a number of different applications. The construction enables automatic manufacturing, which makes it easy and cheap to manufacture. The forces operating on the rotor have their point of attack near the periphery of the machine which result in a long torque arm and consequently high torque. As a result of this, the machine according to the present application have very large torque density. The construction also results in a low starting torque.
The invention according to the present application relates to an electrical machine comprising one or several stators edified by statorpackages, which consist of one or several statorsections. The core of the statorpackage is arranged to cooperate with a coil which winding axis is parallel to the rotary axis to obtain axially directed flux in the machine. Further, the machine comprises one or several rotors that are arranged on a rotary axis. The electrical machine according to the present application may in a preferred embodiment be provided with a ring-shaped statorwinding with large cross section area and small diameter which minimises the waste power and simplifies cooling. Large cross section area and consequently lots of ampere-turns results in high effect per weight and volume unit for the machine.
The stator is edified by statorpackages comprising one or several sections and one coil. The design result in a much shorter path for the magnetic flux compared to earlier known desings because the flux only have to round the cross sections area of the coil. Each statorsection is provided with poles that in a preferred embodiment are placed outside the rotor. The poles of the rotor conduct or block the flux through respective statorsection to obtain an alternating flux through the coil. With many rotorpoles, high frequency is obtained for the generated voltage alternately low rotation speed at motor operation. Each statorsection may be provided with several poles to obtain high frequency at low rotation speed and at the same time provide large fluxarea. The statorcore is made of laminated steel sheets with a statorframe of plastic material. Alternately, the statorcore may be made of compressed powder material.
The rotor is arranged to obtain periodically varying reluctance along its periphery. In a preferred embodiment, the whole rotor is made of magnetic material and the varying reluctance is obtained by providing the rotor with teeth. In this embodiment, the rotor is made of laminated steel sheets, alternately compressed powder material, with low reluctance and low eddy current losses. The rotor may be provided with one outer angled edge which define an envelope surface along its periphery.
In another embodiment, the rotor consist of one or several discs of a non-conducting shape-resistant material with high reluctance such as glass- or carbon fibre armed plastic material. On the surface of the rotordisc, rotorpoles made of material with low reluctance such as powder of metal or laminated steel sheets are mounted. The rotor may be provided with an outer angled edge which define an envelope surface along its periphery. In the latter embodiment, the rotorpoles are mounted on said envelope surface. Within the scope of the attached patent claims, the rotor may be designed in a number of different embodiments.
The rotors and adherent statorpackages of the machine are in a preferred embodiment mounted along the axis of the machine. A multiphase generator or motor is obtained by connecting several rotordiscs with adherent statorpackages on the same axis. To obtain phase difference between the phases the statorpackages may be mounted displaced relative to each other along the periphery. Alternately, the rotordiscs may be displaced relative to each other.
The statorpackages of the machine may be mounted along the periphery of the rotor in an alternative embodiment.
In an embodiment, to obtain large magnet surface the machine is provided with permanentmagnets placed near the envelope surface of the machine, consequently high magnetic flux is obtained. Permanentmagnets are mounted on each statorpole near the envelope surface alternately on the poles of the rotor. The design permits a small distance between the airgap between rotor and stator and the magnets, which result in very low flux leakage. The permanentmagnets are preferably arranged axially directed. The permanentmagnets in the stator are preferably directed to obtain alternately directed flux through the sections of the stator.
The rotors and adherent statorpackages of the machine are in a preferred embodiment mounted along the axis of the machine. The machine may be provided with a device, which separates rotor from adherent statorpackage axially. This will reduce the magnetic brake action when the machine starts as a generator.
The machine may also act as a linear motor or generator. In an alternative embodiment, the machine acts as a linear motor with straight rotor arranged to obtain periodically varying reluctance along its length.
Manufacturing may be automatic to a great extent. In an embodiment, the ring-shaped prefabricated winding is mounted in the stator, subsequently the rotor is mounted as a lid over the winding. Several of these packages may be mounted together and connected to the same axis. Manufacturing will save material since the high torque density results in small volume. The amount of both copper and iron will be reduced correspondingly. The manufacture will not result in waste, which traditional manufacturing with punched stator laminations results in.
Above, a number of examples for applications are mentioned. Generator for car: the invention is smaller, lighter and obtain better charging at low speed than generators according to known technique. Car industry chases weight and the solution provided by the invention will result in a considerably weight loss for the generator. Motor and generator in a vehicle: the invention permits small, light motors that may be integrated in the design of the wheel. High efficiency result in long battery time. Braking result in large brake torque which reduces the need of traditional brakes and also result in effective charging of the battery. High starting torque reduces the need of gearbox. Motor and generator in aeroplanes and satellites: the invention saves both weight and volume, which is very important in these applications. Gearboxes may be eliminated which increases efficiency. The invention may directly replace electrical motors of today, if fed with high frequency ( less than 1 kHz). Reluctance motor for domestic apparatus etc: the invention permits small cheap motors that may be mass produced with small consumption of raw material in an automatic manufacturing process with a minimum of waste. Robots: the invention permits exact movements for robots as a consequence of many poles and synchronous operation. In case of power failure, the robot will stop as a consequence of the high brake torque. The motor may be integrated in the joints of the robot.
The high torque density of the invention is close to the one of the hydraulic motor. The invention may, in many cases, replace these especially if the compressor is electrically operated and the distance is long between the hydraulic pump and the motor.
A method for manufacturing an embodiment of the machine according to the present invention comprises a mould with a lower and an upper part. In the lower part of the mould statorpackages are mounted, or, when manufacturing rotors, rotorpoles. These are mounted in special fixings. Armour may be mounted in the lower part of the mould when desired. The upper part of the mould is fixed in place towards the lower part, subsequently a convenient material, such as plastic material, is pressed into the mould through ducts in the mould.